What is XRF testing? What is the basic principle of XRF testing?

Date：2022-04-15 17:04:17Views：1489

XRF refers to the X-ray fluorescence spectrometer, which can quickly and simultaneously determine multiple elements. Under X-ray excitation, the inner electron of the tested element atom undergoes energy level transition and emits secondary X-rays (X-fluorescence). Observing and describing X-rays from different angles, XRF can be divided into energy scattering X-ray fluorescence spectrometer, abbreviated as EDXRF or EDX, and wavelength scattering X-ray fluorescence spectrometer, abbreviated as WDXRF or WDX, but EDX is widely used in the market. WDX is separated by crystal, and then the diffracted characteristic X-ray signal is received by the detector. If the spectroscopic crystal and the detector move synchronously and constantly change the diffraction angle, the wavelength of characteristic X-rays produced by various elements in the sample and the intensity of X-rays at each wavelength can be obtained for qualitative and quantitative analysis. EDX uses an X-ray tube to generate primary X-rays, which are irradiated on the sample, and the generated characteristic X-rays enter the Si (LI) detector for qualitative and quantitative analysis. EDX has small volume, relatively low price and fast detection speed, but its resolution is not as good as WDX.

XRF uses the physical principle to detect the elements of substances, which can be analyzed qualitatively and quantitatively. That is, the X-ray penetrates the internal electrons of the atom, and the characteristic X-ray is generated by the external electron supply. The content information of each element can be obtained according to the intensity of the characteristic X-ray of the element. This is the basic principle of X-ray fluorescence analysis. It can only measure elements, not compounds. However, because XRF is surface chemical analysis, the measured samples must meet many conditions, such as smooth surface and uniform composition. If the composition is uneven, it can only indicate that the composition of the micro region measured by XRF is so, and others cannot be expressed.

Advantages of XRF:

High analysis speed. The determination time is related to the determination accuracy, but it is generally very short. All elements in the sample can be measured in 2-5 minutes.

Non destructive. In the determination, it will not cause the change of chemical state, nor will the sample fly away. The same sample can be measured repeatedly, and the results have good reproducibility.

High analytical precision.Sample preparation is simple, and solid, powder and liquid samples can be analyzed.

The range of test elements is large. WDX can detect b5-u92 at ppm-100%, while EDX can detect most elements, na11-u92, at 1ppm-100ppm. In addition, be content in Cu alloy can be detected.

It can quantitatively analyze the element composition of materials with high resolution, and the probe size is 500 μ m (WDX), 75 μ m (EDX)。

Physical principle of X-ray fluorescence:

X-ray is an electromagnetic wave within a specific wavelength range in the electromagnetic spectrum. Its characteristics are usually described by energy (unit: keV) and wavelength (unit: nm).

X-ray fluorescence is a phenomenon caused by changes in atoms. A stable atomic structure consists of nuclei and extra nuclear electrons. The electrons outside the nucleus run on their own fixed orbits with their own unique energy. The inner electrons (such as k-layer) break away from the bondage of atoms and are released under the irradiation of X-rays with sufficient energy. The gradual release of electrons will lead to the corresponding electron vacancy in the electron shell. At this time, the electrons in the high-energy electron shell (such as L-layer) will transition to the low-energy electron shell to fill the corresponding electron vacancy. Due to the energy gap between different electron shells, these energy differences are released in the form of secondary X-rays, and the secondary X-rays released by different elements have specific energy characteristics. This process is what we call X-ray fluorescence (XRF).

Wavelength of X-ray

The atoms of elements are excited by high-energy radiation, which causes the transition of inner electrons and emits X-rays with a certain specific wavelength. According to Mosley's law, the wavelength of fluorescent X-rays is λ It is related to the atomic number Z of the element, and its mathematical relationship is as follows:

λ= K(Z− s) −2

Where K and s are constants.

X-ray energy

According to quantum theory, X-ray can be regarded as a particle flow composed of a quantum or photon, and the energy of each light is:

E=h ν= h C/ λ

Where, e is the energy of X-ray photons, in keV; H is Planck constant; ν Is the frequency of light wave; C is the speed of light.

Therefore, as long as the wavelength or energy of fluorescent X-ray is measured, the types of elements can be known, which is the basis of qualitative analysis of fluorescent X-ray. In addition, there is a certain relationship between the intensity of fluorescent X-ray and the content of corresponding elements. Therefore, element quantitative analysis can be carried out.

Application and analysis of X-ray fluorescence:

a) X-ray for elemental analysis is a new analytical technology, but after more than 20 years of exploration, it has now become fully mature and has become a widely used in metallurgy, geology, nonferrous metals, building materials, commodity inspection, environmental protection, health and other fields.

b) The characteristic X-ray intensity of each element is not only related to the energy and intensity of the excitation source, but also related to the content of this element in the sample.

c) According to the characteristic X-ray intensity of each element, the content information of each element can also be obtained. This is the basic principle of X-ray fluorescence analysis.

I believe that by reading the above content, you have a preliminary understanding of XRF test. At the same time, I hope you can make a summary in the learning process, so as to continuously improve your professional level. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing organization for electronic components in China. It has three standardized laboratories with an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, identification of IC authenticity, product design, material selection, failure analysis, function testing, factory incoming material inspection, X-ray testing of components, tape braiding and other testing items.